1. Field of the Invention
The present invention relates generally to optical fiber, and more particularly to dispersion compensation fiber and transmission systems including coupled combinations of transmission fiber and dispersion compensation fiber.
2. Technical Background
Higher data rates and wider bandwidth systems are becoming needed for the telecommunications industry. Thus, the search for high performance optical fibers designed for long distance, high bit rate telecommunications that operate over broad bandwidths has intensified. These high data rates and broad bandwidths, however, have penalties associated with them. In particular, dispersion is a significant problem in such systems. More specifically, positive dispersion builds along the length of the high data rate transmission fiber. Dispersion compensating fibers included in cable or in dispersion compensation modules have been designed that compensate for such dispersion. These fibers generally have negative dispersion slope and negative total dispersion within the operating wavelength band, with the dispersion having a large negative value such that a short length of the dispersion compensating fiber compensates for the positive dispersion and positive slope of the longer transmission portion. In operation, the bend performance (both macro-bending and micro-bending) and other properties, such as dispersion, kappa (kappa being the ratio of total dispersion divided by dispersion slope at a specific wavelength), cutoff wavelength and effective area of the dispersion compensating fiber are important and generally competing criteria.
A class of transmission fibers that have utility in transmission systems has been developed recently, such fibers being generally referred to herein as moderate dispersion, low dispersion slope fibers (MDLDSF). In particular, U.S. Pat. App. No. 60/437,291 filed Dec. 31, 2002 describes one such MDLDSF. In particular, such fibers have dispersions between about 4 and 8 ps/nm/km at 1550 nm, and dispersion slope of less than 0.025 ps/nm2/km for all wavelengths between about 1525 and 1625 nm.
Thus, there is a need for a dispersion compensating fiber which: (1) exhibits desired properties over a desired wavelength range, (2) retains high performance optical fiber characteristics such as high strength, low attenuation, acceptable resistance to micro- and macro-bend induced loss, and sufficient effective area and cutoff wavelength, and (3) is particularly effective at compensating for accumulated dispersion in systems utilizing such MDLDSF across the operating wavelength range such that relatively low average residual dispersion results in the system.